Combustion apparatus including pneumatically suspended combustion zone for waste material incineration and energy production

ABSTRACT

High temperature combustion apparatus incorporating a pneumatically suspended combustion zone and capable of supporting relatively high combustion temperatures, in excess of 2400° C. (4352° F.) for essentially total combustion with minimal pollutant production. The combustion apparatus may be employed for waste material incineration in general, toxic waste incineration, and for smokeless burning of wood and vegetation. The combustion apparatus may be employed in an efficient steam electric power generating plant which employs municipal solid waste as fuel, and/or in combination with a magnetohydrodynamic (MHD) electric generator. The pneumatically suspended combustion zone is created by having streams of combustion air directed upwardly from a floor grate and from the sides of a combustion chamber such that combustion occurs in a swirling turbulent mass which does not directly contact either the walls or the floor of the combustion chamber. The relatively high combustion temperatures are sustained by providing a high volume of excess combustion air, the same combustion air which maintains the pneumatically suspended combustion zone. High combustion temperatures are contained with little use of refractory materials, and without melting the combustion chamber sidewalls.

BACKGROUND OF THE INVENTION

The present invention relates generally to combustion apparatus forwaste material incineration in general, toxic waste incineration, refuseburning, and power generation, and, more particularly, to combustionapparatus capable of supporting combustion temperatures in excess of2400° C. (4352° F.) for essentially total combustion with minimalpollutant production.

Incinerator/furnace/boiler combustion chamber designs presentlyavailable for applications such as municipal solid waste disposal,industrial solid waste disposal, toxic waste disposal, coal and oilfired electric power generating plants, and the like, include combustionchambers made of refractory materials such as fire brick, which aregenerally limited to an approximately 1300° C. (approximately 2400° F.)maximum combustion temperature. Although higher temperature refractorymaterials are available, their cost is prohibitive for mostapplications.

It is, however, desirable to employ even higher combustion temperatures.Higher combustion temperatures offer a number of advantages. Highercombustion temperatures in general result in more complete burning,reducing the need for exhaust gas scrubbing. There is the potential fortotally combusting toxic materials, reducing the need for exhaust gasscrubbing following toxic waste incineration. In steam power generationapplications, higher combustion temperatures in addition result in moreefficient operation. Steam temperatures in excess of approximately 980°C. (approximately 1800° F.) are particularly efficient. Anotheradvantage of high combustion temperatures, particularly in the contextof municipal trash incineration, is that light gauge metal objectscontained in the solid waste materials are melted by the exposure toextreme temperatures. These light gauge metal objects ultimately becomesmall pieces of metal which are easily carried away as ash.

SUMMARY OF THE INVENTION

It is accordingly an object of the invention to provide combustionapparatus capable of supporting relatively high combustion temperatures,in excess of 2400° C. (4352° F.).

It is another object of the invention to provide such apparatus in whichthe use of refractory materials in combustion chamber construction isminimized.

It is another object of the invention to provide a highly efficient andnon-polluting municipal waste incinerator, thus substantially reducinglandfill usage.

Another object of the invention is to provide efficient combustionapparatus for retrofit to existing coal or oil fueled power generationplants such that municipal solid waste can be used as a fuel for powergeneration.

Briefly, and in accordance with an overall aspect of the invention, hightemperature combustion apparatus incorporates a pneumatically suspendedcombustion zone created by having streams of combustion air directedupwardly from a floor grate and from the sides of a combustion chambersuch that combustion occurs in a swirling turbulent mass which does notdirectly contact either the walls or floor of the combustion chamber.Relatively high combustion temperatures are sustained by providing ahigh volume of excess combustion air, the same combustion air whichmaintains the pneumatically suspended combustion zone. High combustiontemperatures can be contained with little use of refractory materials,and without melting the combustion chamber sidewalls.

In one particular embodiment of the invention, combustion apparatusincludes walls defining a combustion chamber having a pneumaticallysuspended combustion zone, and at least portions of the walls are formedof a plurality of adjacent tubes having tube interiors and tube walls.At least one tube supply blower is connected to the tubes forpressurizing the tube interiors with combustion-supporting gas, such asair. The tube walls have openings, such as slots, oriented generallytowards the combustion zone, and the tubes and slots extendhorizontally. Preferably, the openings are oriented so as to induceswirling gas flow movement within the combustion zone.

Thus combustion-supporting gas streams are directed out of the openingsto at least partially define the combustion zone and to force the heatof combustion away from the walls. Typically, the tubes comprise metal,and at least portions of the walls are free of refractory materials.However, in some embodiments, the tubes comprise a refractory material,such as silicon carbide.

Preferably, the tubes forming the walls of the combustion chamber arespaced from each other, and there is an outer containment structuresurrounding the combustion chamber walls. At least one outer containmentstructure supply blower is connected for pressurizing the outercontainment structure with combustion-supporting gas, such as air, sothat combustion-supporting gas streams are directed between the tubesinto the combustion chamber, in addition to the combustion air streamsdirected out of the tube slots. Vanes preferably are affixed to thetubes for controlling the direction of combustion-supporting gas streamsdirected between the tubes.

The outer containment structure preferably is subdivided into aplurality of outer containment zones supplied by separate blowers suchthat combustion air is supplied at different rates from different zonesto facilitate adjustment of combustion parameters.

In one embodiment, the combustion apparatus takes the form of atunnel-like structure wherein solid waste material is introduced nearone end by a solid waste material supply conveyor and travels towardsthe other end where there is an exhaust gas port and an ash conveyorexit. The ash conveyor, also termed a combustion chamber conveyor,includes conveyor elements which are driven over a floor grate havingspaced grate elements between which combustion-supporting gas streamsare directed upwardly. The combustion chamber conveyor serves to conveyheavy objects through the combustion apparatus, as well as to conveynon-combusted particles to an ash collection system. In addition, anentry point for hydrocarbon fuel such as oil or powdered coal may beprovided near where solid waste material is introduced.

A chamber defining an outer containment zone is mounted at the one endof the combustion chamber, directly opposite the exhaust port.Pressurized combustion air is forced into this chamber at a relativelyhigher volume compared to other areas of the outer containment structurein order to force the swirling turbulent motion of the combustionprocess away from the solid waste conveyor entry point and thehydrocarbon fuel entry point, towards the opposite end of the combustionchamber to the exhaust gas port and ash conveyor exit.

Another aspect of the invention is the preheating of solid wastematerial to nearly its flash point before introduction into thecombustion chamber. In one embodiment, the solid waste material supplyconveyor runs within a pressurized chamber, and includes conveyorelements moving over a grate, with hot combustion-supporting gasdirected upwardly through the grate. The pressurized chamber has arevolving door type entry door which receives waste material, whilemaintaining pressure within the pressurized chamber. Higher pressure ismaintained within the pressurized waste material supply conveyor chamberthan in the combustion chamber, resulting in pneumatically assistedinjection of waste material into the combustion chamber.

In another embodiment of the invention, the combustion chamber wallsinclude a multiplicity of openings oriented generally towards thecombustion zone, and there is at least one blower in gas flowcommunication with these openings for directing combustion-supportinggas through the openings to at least partially define a combustion zoneand to force the heat of combustion away from the walls. Preferably, anouter containment structure surrounds the walls, and the blower isconnected for pressurizing the outer containment structure withcombustion-supporting gas, such as air, so that combustion-supportinggas is directed from within the outer containment structure through theopenings. In this particular embodiment, the combustion chamber wallspreferably comprise refractory materials.

BRIEF DESCRIPTION OF THE DRAWINGS

While the novel features of the invention are set forth withparticularity in the appended claims, the invention, both as toorganization and content, will be better understood and appreciated,from the following detailed description, taken in conjunction with thedrawings, in which:

FIG. 1 is a side elevational view of a solid waste incinerator system inoverview, including combustion apparatus in accordance with theinvention in the form of a tunnel type combustion chamber;

FIG. 2 is a three dimensional representation of tube walls defining acombustion chamber, and including a pressurized air supply system;

FIG. 3 is a top view, with portions cut away, of the combustionapparatus of FIG. 1;

FIGS. 4A and 4B are longitudinal sections, respectably taken on lines4A--4A and 4B--4B of FIG. 3;

FIG. 5 is an enlarged view of the left side of FIG. 4B;

FIG. 6 is a lateral cross section taken on line 6--6 of FIGS. 3, 4A and4B;

FIG. 6A is an enlarged view of portion 6A--6A of FIG. 6;

FIG. 7 is a similar lateral cross section taken on line 7--7 of FIGS. 3,4A and 4B;

FIG. 8 is a view similar to that of FIG. 6, showing further details ofthe waste material supply conveyor structure;

FIG. 9 is a view taken generally along line 9--9 of FIG. 8 showingfurther details of the material supply conveyor structure;

FIG. 10 is an end view, partly in section, of a second embodiment of theinvention, in the form of a vertically-extending incinerator primarilyfor wood and vegetation debris;

FIG. 11 is a view, looking down, taken on line 11--11 of FIG. 10; and

FIG. 12 is a cross-sectional representation of an alternative combustionchamber wall construction.

DETAILED DESCRIPTION

Referring initially to FIG. 1 for an overview, a solid waste materialincinerator system 20 embodying the invention includes high temperaturecombustion apparatus, generally designated 22, having a solid wastematerial entry port 24, a hot exhaust gas exit port 26, an exhaust gassystem generally designated 28, a flue 29 connecting the port 26 to theexhaust gas system 28, and an ash collection system, generallydesignated 30. The exhaust gas system 28 comprises, for example, a heatexchanger, a boiler for generating steam for power and/or amagnetohydrodynamic (MHD) electric generator.

The combustion apparatus 22 more particularly comprises a horizontal,tunnel-like combustion chamber 32 within which a pneumatically-suspendedcombustion zone 33 is defined, and an outer containment structure 34. Inthe embodiment of FIG. 1, the combustion chamber 32 has walls made ofadjacent tubes, described hereinbelow in detail with reference to FIGS.2, 3, 4A, 4B, 5, 6 and 7, and the interiors of these tubes arepressurized by tube supply blowers. By way of example, a total of eighttube supply blowers are provided, blowers 40, 42, 44 and 46 visible inFIG. 1, and additional tube supply blowers 48, 50, 52 and 54, describedhereinbelow with reference to FIG. 2. Pressurized by these eight tubesupply blowers are four main tube supply ducts 56 and 58 (FIGS. 1 and 2)and 60 and 62 (FIG. 2).

In addition, at least one outer containment supply blower 64 isprovided, connected for pressurizing the outer containment structure 34.Preferably, the outer containment structure 34 is zoned, and there isthus at least one additional outer containment structure blower 66 tofacilitate individual zone airflow control.

Within the combustion apparatus 22 is an air-cooled combustion chamberconveyor system 70, also termed an ash conveyor system, which serves thedual purposes of conveying heavy objects through the combustionapparatus 22, which heavy objects are too heavy for the pneumaticallysuspended combustion zone 33, and of conveying non-combusted particlesto the ash collection and treatment system 30.

With reference now to FIG. 2 in particular, the combustion chamber 32 isdefined by walls comprising longitudinally mounted slotted steel tubespressurized by the eight tube supply blowers 40, 42, 44, 46, 48, 50, 52and 54 via the main tube supply ducts 56, 58, 60 and 62. Moreparticularly, in the FIG. 2 orientation the near sidewall 100 of thecombustion chamber 32 comprises a plurality of adjacent slotted walltubes 101 connected for pressurization by the tube supply blowers, andthe far sidewall 102 of the combustion chamber 32 comprises anotherplurality of adjacent slotted wall tubes 103 likewise connected forpressurization by the tube supply blowers. An inlet end endwall 104 ofthe combustion chamber 32 comprises a plurality of pressurized adjacentslotted wall tubes 105, and an outlet end endwall 106 of the combustionchamber 32 comprises a plurality of slotted wall tubes 107. Similarly,the top or ceiling 108 of the combustion chamber 32 comprises aplurality of pressurized adjacent slotted ceiling tubes 109, likewiseconnected for pressurization by the tube supply blowers.

For supplying the interior of the slotted wall and ceiling tubes 101,103, 105, 107 and 109, connected to the four main tube supply ducts 56,58, 60 and 62 are secondary tube supply ducts 112, 114, 116, 118 and 120for the near sidewall 100, extending vertically between supply ducts 56and 58; secondary tube supply ducts 122, 124, 126, 128 and 130 for thefar sidewall 102, extending vertically between main supply ducts 60 and62; and secondary supply ducts 132, 134, 136, 138 and 140 for theceiling 108, extending horizontally between respective pairs 112,122;114,124; 116,126; 118,128 and 120,130 of the vertically extendingsecondary supply ducts. The secondary supply ducts 112 and 122additionally supply the slotted tubes 105 of the inlet end endwall 104,and the secondary supply ducts 120 and 130 additionally supply theslotted tubes 107 of the outlet end endwall 106. The slotted wall andceiling tubes 101, 103, 105, 107 and 109 are connected between thevarious secondary tube supply ducts as represented in FIG. 2.

It will be appreciated that the particular tube supply arrangementdepicted in FIG. 2 is representative only, and is subject to widevariation in particular designs embodying the invention. For example,different numbers of tube supply blowers may be employed, the ductingsystem may differ, and zone control over the pressure within differentportions of the tube wall structure may be employed.

The actual construction of the combustion apparatus 22 will now bedescribed in greater detail with reference to FIGS. 3, 4A, 4B, 5, 6 and7.

As noted hereinabove, the invention eliminates or reduces the need forrefractory materials to contain the extreme temperatures produced in thecombustion chamber 32 by employing the pneumatically suspendedcombustion zone 33, generally represented by its center in the lateralcross section of FIG. 6. In overview, pressurized air from the slottedsidewall tubes 101 and 103, the end wall tubes 105 and 107 and theceiling tubes 109 supplies a high volume of combustion air, andadditionally keeps the heat of combustion away from the walls.

More particularly, and with particular reference to the lateral crosssections of FIGS. 6 and 7, the walls of the tubes 103 comprising thecombustion chamber 32 far sidewall 102 have slots 144 oriented generallytowards the combustion zone 33, the walls of the tubes 101 comprisingthe combustion chamber 32 near sidewall 100 have slots 146 orientedgenerally towards the combustion zone 33, and the walls of the tubes 109comprising the combustion chamber 32 ceiling 108 have slots 148,likewise oriented generally towards the combustion zone 33. FIG. 4B andthe enlarged FIG. 5 show the slots 144 of the far sidewall 102 tubes 103as viewed from the interior of the combustion chamber 32, and inaddition show, in cross section, slots 150 in the walls of the tubes 105comprising the inlet end endwall 104. FIG. 7, in addition to the slots144, 146 and 148 in the tubes 103, 101 and 109 respectively comprisingthe combustion chamber 32 sidewalls 102 and 100 and ceiling 108, showstwo columns of slots 152 and 154 in the walls of the tubes 107comprising the outlet end endwall 106, also oriented generally towardsthe combustion zone 33.

To promote swirling gas flow motion within the combustion zone 142, theslots 144, 146 and 148 in the wall and ceiling tubes 103, 101 and 109are generally oriented at an angle with reference to the perpendiculardirection of the walls 102 and 100 and ceiling 108 such that airflow isdirected as indicated by the various arrows in FIGS. 6 and 7.

The combustion chamber 32 inlet end and outlet end endwalls 104 and 106have different slot arrangements to promote swirling gas flow motionwithin the combustion zone 142. As may be seen in FIG. 7, the columns ofslots 152 and 154 in the walls of the tubes 107 comprising the outletend endwall 106 are respectively oriented upwardly and downwardly,consistent with the orientation of the slots 144 and 146 in the tubes103 and 101 of the respectively adjacent sidewalls 102 and 100.

The slots in the walls of the tubes 105 comprising the inlet end endwall104 are correspondingly oriented in a manner which promotes the swirlinggas flow motion within the combustion zone 142. Thus, in thelongitudinal sections of FIGS. 4B and 5, particularly the enlarged viewof FIG. 5, the particular slots 150 which are depicted in the tubes 105comprising the inlet end endwall 104 are nearest the far sidewall 102,and accordingly are oriented upwardly. Although not specificallyillustrated, those portions of the tubes 105 nearest the near sidewall100 have slots which are oriented upwardly.

In addition to the slots 144, 146, 150, 152 and 148 in the tubescomprising the combustion chamber 32 walls 102, 100, 104 and 106 andceiling 108, there is a slotted floor grate 160 (FIG. 6) mountedlongitudinally and comprising the top of a floor grate plenum chamber162. The floor grate plenum chamber 162 has a bottom wall 164, andsidewalls 166 and 168, and is pressurized by means of a separate blower(not shown) and a plenum chamber supply duct system includinglongitudinal ducts 170 and 172 (FIG. 6) running along either side, andconnected to the floor grate plenum chamber 162 through respective setsof supply ports 174 and 176. For convenience of illustration, in FIGS.4A and 4B the floor grate plenum chamber 162 supply ports 174 and 176are shown as circular openings in the respective floor grate plenumchamber 162 sidewalls 166 and 168. FIG. 4B happens to be taken on asection intermediate a pair of floor grate 160 elements, and a sidesurface 160' of one of the floor grate elements 160 is accordinglyvisible in FIG. 4B. The floor grate elements 160 by way of examplecomprise strips of steel 1/4 inch thick and three inches wide orientedon edge and running substantially the entire length of the combustionchamber 32, up to a terminating point 178 near the outlet end, where asolid slab 180 of refractory material (FIGS. 4B and 7) is employed tofacilitate ash collection.

Air flowing upwardly from the flow grate plenum chamber 162 servesseveral purposes, including aiding in pneumatic suspension of thecombustion zone 33, contributing to the supply of excess combustion air,cooling the flow grate 160, and cooling the conveyor 70.

In addition to the air supply for the slotted wall tubes 101, 103, 105,107, ceiling tubes 109 and floor grate 160, the outer containmentstructure 34 has an interior 190 which is pressurized with combustionair by means of a representative and appropriately connected outercontainment structure supply blower 192. Thus, combustion air isdirected between the wall and ceiling tubes 101, 103, 105, 107 and 109into the combustion chamber 32. The combustion air directed between thewall and ceiling tubes is in addition to combustion air directed fromthe tube interiors through the tube slots 144, 146, 148, 150 and 152,and serves the dual purposes of providing additional cooling for thetubes and facilitating control over the combustion process. The slottedwall and ceiling tubes 101, 103, 105, 107 and 109, while adjacent,accordingly are spaced from each other to accommodate the passage ofcombustion air therebetween. A typical spacing is 1/8 inch between tubeswhich are eight inches in diameter.

Preferably, the outer containment structure 34 is zoned so that airvolume may readily be adjusted through different portions of thecombustion chamber 32 walls 100, 102, 104 and 106, and ceilings 108.

Thus, and with reference to FIGS. 3, 4A and 4B, an outer containmentstructure zone is defined by an outer containment substructure orchamber 194 (FIGS. 3 and 4A) having a pressurized interior 196 (FIG. 4B)and supplied with combustion air by means of a zone blower 198. Thechamber 194 is mounted at the end of the combustion chamber 32 directlyopposite the exhaust port 26. Pressurized ambient air is forced into thechamber 194 and then between the tubes 105 of the inlet end endwall 104at a higher volume compared to any other portion of the outercontainment structure 34 in order to force the swirling turbulent motionof the combustion zone 33 away from the solid waste conveyor entry point24 (where hydrocarbon fuel may also be introduced), towards the oppositeend of the combustion chamber 32 to the exhaust port 26 and conveyor 70exit.

As described hereinabove, the tube slots 144, 146, 148, 150 and 152 areoriented so as to promote swirling gas flow motion within the combustionzone 33. In addition, affixed to and positioned generally between thewall and ceiling tubes 101, 103, 105, 107 and 109 are airflow-directingvanes, represented in the enlarged view of FIG. 6A, as vanes 200. Thevanes 200 correspond in orientation with the slots of the particulartubes to which the vanes 200 are affixed, thus reinforcing andaugmenting the promotion of swirling gas flow motion. In addition, thevanes 200 direct airflow over the outsides of the tubes, cooling thetubes, as well as providing an air curtain effect further insulating thetubes and reducing erosion.

In this regard, it will be appreciated that the combustion air forcedfrom the containment zone chamber 194 between the slotted tubes 105comprising the inlet end endwall 104 at a relatively higher volumecompared to other portions of the outer containment structure 34, inconjunction with vanes 200 affixed to the slotted tubes 105, aids inpromoting the swirling motion of the combustion zone 142 at the outset.

Another outer containment structure zone is defined by a chamber 202(FIG. 6) having an interior 204 and pressurized by means of a duct entrypoint 206 located immediately below the solid waste material entry port24, which is supplied with preheated solid waste material by a solidwaste conveyor system, generally designated 208, described hereinbelowwith reference to FIGS. 8 and 9. The outer containment structure zonedefined by the chamber 202 forces combustion air into the combustionchamber 32 between somewhat enlarged slotted wall tubes 210 in thisparticular region. These wall tubes 210 are enlarged for the purpose ofproducing a high velocity air stream which, by pneumatic assist, propelspieces of solid waste material into a circular pattern. Thus, as solidwaste is injected through entry port 24 downwardly into the combustionchamber 32, pieces of solid waste material free fall into the highvelocity air stream and are propelled horizontally towards the oppositeside 102 of the combustion chamber 32, where the pieces encounter anupwardly flowing air stream from the slots 144 in the tubes 103, thusbeginning the circular pattern of the combustion process. In addition,hydrocarbon fuel in the form of powdered coal may be introduced throughthe chamber 202.

Represented generally by element 212 in FIG. 6 are conventional fuelsupply and ignition devices, such as gas supply jets (propane or naturalgas), oil injection nozzles, and spark gaps. Typically these devices 212are located immediately below the solid waste material entry port 24,but may be at any point or points within the combustion chamber 32.Advantageously, gas supply jets and sparking devices are mounted atvarious locations along the lower portion of the combustion chamber 32.

As noted hereinabove, there is an air-cooled combustion chamber conveyorsystem 70 or ash conveyor 70 which serves the dual purposes of conveyingheavy objects and of conveying non-combusted particles through an ashexit port 218 to the ash collection and treatment system 30. Theconveyor 70 more particularly comprises a series of conveyor elements inthe form of laterally extending angle irons 220 affixed at either end toa pair of conveyor chains 222 driven by sprockets represented at 224 and226. The angle irons 220 also serve as scraper elements. Preferably, thechains 222 are the type commonly employed for driving the tracks oftracked vehicles, and which accordingly have attachment points suitablefor the angle irons 220. Although not illustrated, in order to avoidoverheating of the chains 222, preferably there is a chain channel intowhich cooling air is injected. The conveyor 70 is driven by one or morevariable speed, reversible electric or hydraulic motors (not shown).Conveyor 70 speed may vary according to the type and size of wastematerial being combusted.

Ash collection is facilitated by the solid slab 180 of refractorymaterial (FIGS. 4B and 7) in the floor of the combustion chamber 32 nearthe outlet end endwall 106. Thus, unlike the region above the slottedfloor grate 160 with its upwardly-directed airflow, ash 224 is free tosettle onto the slab 180, as is represented in FIG. 7, to be pushed bythe conveyor 70 angle irons 220 into the ash collection system 30. Inaddition, centrifugal force generated by the generally circular gas flowmotion of the swirling combustion zone 33, aided by gravity, assists inthe deposition of ash 224 on the refractory material slab 180 forconveying into the ash collection system 30.

Very briefly, the ash collection system 30 includes a primary ashcollection compartment 230 and a secondary ash/metal collectioncompartment 232 wherein combustion gases are mixed with air drawnthrough a vent 234, and additionally are cooled by a water spray or mist236. There are several additional secondary ash/metal separationcompartments 238 and 240, upper baffles 242 and 244, lower baffles 246and 248, and an alternate media filter system 250 through which themixture of air and combustion gases is drawn by an ash collection blower252. The ash collection blower 252 forces the air/gas mixture through aduct 254 to an exhaust gas flue. The secondary ash/metal separationcompartments 232, 238 and 240 and the filter system 250 includecollection hoppers equipped with waste gates (not shown) designed formanual or automatic opening devices. The alternate media filter system250 includes a set of filter media panels 256 mounted on a horizontaltrack 258 between a collection compartment 260 and a filter backwashcompartment 262. The filter media panels 256 can be moved one at a timeinto the filter backwash compartment 262 for selective cleaning, whilemaintaining operation.

Referring now in addition to FIGS. 8 and 9, the solid waste materialconveyor system 208 serves generally to introduce appropriately-sized,preheated solid waste material into the tunnel-like combustion chamber32. The solid waste material is introduced through the port 24, which islocated in the near sidewall 100 near the inlet end endwall 104, at theopposite end with respect to the outlet end endwall 106 having the hotexhaust gas exit port 26 and the ash collection and treatment system 30.Solid waste material, in addition to falling by gravity from theconveyor system 208 into the combustion chamber 32, preferably isinjected by pneumatic assist. The solid waste entry port 24 is sized toaccommodate the type and size of solid waste objects injected into thetunnel-like combustion chamber 32. For example, forest waste productsand municipal foliage waste may range in size up to eighteen inchescross-sectional diameter and seventeen inches in length. Baggedhousehold garbage and trash objects up to thirty inches cross-sectionaldiameter may be injected into the tunnel-like combustion chamber. Solidwaste objects exceeding these cross-sectional diameters are shredded byemploying a hammermill type shredder 270 driven by a motor 272.

More particularly, the solid waste material conveyor system 208 includesa primary waste material supply conveyor 274 of any convenientconstruction, and terminating at a roller 276, which introduces solidwaste material along an inclined chute 278 into the hammermill shredder270.

A secondary waste material supply conveyor 280 communicates directlywith the interior of the combustion chamber 32 through the port 24, andis contained within a heated and pressurized tunnel-like duct 282. Thesecondary waste material supply conveyor 280 is essentially identical inconstruction to the combustion chamber conveyor 70, and thus includes aseries of angle iron conveyor elements 284 connected to chains driven bysprockets 286, in turn driven by a variable speed motor (not shown). Theconveyor elements 284 move along a slotted floor grate 288, similar inconstruction to the floor grate 160 of the combustion chamber conveyor70. Below the floor grate 288 is a pressurized plenum chamber 290, whichprovides pressure for propelling hot air to preheat waste material, andfor slightly pressurizing the duct 282 to provide airflow forpneumatically assisted injection of waste material into the combustionchamber 32. Thus, to provide pneumatic assist for solid waste materialinjection through the port 24, a higher pressure is maintained in thetunnel-like waste material supply conveyor duct 282 compared to thecombustion chamber 32.

To maintain a pressure differential between the interior of thetunnel-like duct 282 and the ambient, while permitting the introductionof shredded solid waste material, a revolving door type structure 292 isprovided having vanes 294 rotating within a generally cylindricalhousing 296. The cylindrical housing 296 has an entry port 298 and anexit port 300, which delivers shredded solid waste material to thesecondary waste material conveyor 280.

It is a feature of the invention that waste material moving along thesecondary supply conveyor 280 is preheated prior to being introducedinto the combustion chamber 32. Thus, heated air is forced from theplenum chamber 290 below into and around the shredded solid wastematerial as material moves along the slotted floor grate 288 towards thecombustion chamber 32. At the very least this accomplishes drying andheating of the shredded solid waste material. Preferably, thetemperature of shredded solid waste material is raised to a temperaturenear its flash point as the solid waste material is injected into thecombustion chamber 32 by gravity and pneumatic assist.

There is an element for providing hot air for waste material preheatingin the representative form of a heat exchanger 300 within the combustionchamber 32. The heat exchanger 300 may comprise a tube of hightemperature refractory material, or a steel pipe with a refractorymaterial protective coating. The heat exchanger 300 may alternatively belocated within the exhaust gas system 28 or the flue 29 (FIG. 1).Although less efficient, a separately-fueled heater (not shown) may beemployed instead of the heat exchanger 300. In the illustratedembodiment, a blower 302 on the inlet (cold) side of the heat exchanger300 is provided to force ambient air through the heat exchanger 300, anda hot air duct 304 connects the outlet side of the heat exchanger 300 tothe plenum chamber 290 below the secondary waste material supplyconveyor 280 running within the heated tunnel-like duct 282.

As noted hereinabove with reference to FIG. 1, the exhaust gas system 28comprises, for example, a heat exchanger, a boiler for generating steamfor power and/or a magnetohydrodynamic (MHD) electric generator. MHDelectric power generation and a steam turbine may be employed in tandem.MHD electric power generation requires relatively high gas temperaturesto achieve thermal ionization so that the gas is sufficientlyconductive, and the combustion apparatus of the invention achieves suchtemperatures. In addition, the threshold temperature for ionization canbe lowered by appropriately "seeding" the hot gas flowing through an MHDelectric generator, and the invention advantageously inherently canprovide such "seeding" due to various constituents present in municipalsolid waste.

In most cases, the exhaust gas system 28 will include an exhaust gasscrubber of appropriate configuration. Typically, an electrostaticprecipitator is employed to remove fly ash. In applications wherecombustion apparatus of the invention is retrofitted to convert existingcoal-fired power plants, no additional equipment is necessary forpreparing exhaust gases for entry into the atmosphere; existing exhaustgas scrubbing equipment can be retained.

For operation, the combustion process is begun by injecting hydrocarbonfuel through the chamber 202 or oil injection nozzles, solid wastematerial through the entry port 24, or both, along with gas assist(propane or natural gas), ignited by sparking devices represented aselement 212. Once temperatures reach a level where the combustionprocess is self-sustaining, the gas assist is turned off. Thus, oncecombustion temperatures reach approximately 1500° F. (approximately 800°C.), the combustion of coal and solid waste material begins immediatelyupon injection into the combustion chamber 32.

Relatively large mass solid waste material objects, such as objectsexceeding two pounds and cross-sectional diameters of six inches ormore, which are injected into the combustion chamber 32 generally freefall to the combustion chamber conveyor 70, whereupon exposure toextreme temperatures causes combustible material to rapidly explode fromthe object surface. Large mass objects are thus converted into superheated gas which becomes part of the swirling turbulent combustion zone33, and travels longitudinally along the combustion chamber 32.

Lightweight combustible objects injected through the entry port 24, suchas cardboard, paper, plastics and household garbage, move towards thecenter of the combustion chamber 32 by pneumatic assist. As combustionoccurs, these lightweight combustible objects move in the swirlingturbulent combustion zone 33 through the combustion chamber 32.Combustion is complete prior to the exit of combustion gases through theexhaust port 26.

Thus, combustible solid waste material is totally consumed by combustiontemperatures in excess of 2400° C. (4352° F.), which are achieved as aresult of the high volume of excess combustion air.

Noncombustible metal objects such as steel cans and steel tire rims andwheels become molten, and eventually free fall by gravity into the ashcollection system 30 from the discharge end of the air cooled conveyor70.

These noncombustible particles, other than fly ash and molten metalparticles, settle as represented at 224 to the non-slotted portion 180of the combustion chamber 32 floor made of refractory material, assistedin part by centrifugal force created by the circular motion of the gasflow within the combustion zone 33. The angle iron conveyor scraperelements 220 move the noncombustible particles 224 through the ash exitport 218 into the primary ash collection compartment 230 by gravity andpneumatic assist. Combustion gases are drawn from the combustion chamber32 through the ash exit port 218 providing pneumatic assist to thenon-combusted particles. The noncombustible and molten metal particlesthen fall by gravity and pneumatic assist into the secondary ash andmetal separation/collection compartment 232. Air is drawn from the vent234 which cools the molten metal as the metals fall by gravity.

Lighter non-metallic particles are drawn by pneumatic assist into thesecondary compartment 232. Within the secondary compartment 232 thewater mist 236 is sprayed downward into the non-combusted particles asthe particles move through the compartment 232 and over the baffle 246.The particles accordingly absorb the liquid, and some become heavyenough to fall by gravity into the collection hopper below, rather thanbeing carried by the gas stream.

This process is repeated as non-combusted particles pass through thebaffles and are subjected to a similar misting process in thecompartments 238 and 240. The mixture of air and combustion gaseseventually reaches the alternate media filter system 250, drawn by theblower 252, and passes as particulate-free gas through the flue 254.

It will be appreciated that the solid waste incinerator system 20 ofFIGS. 1-9 can be employed for power generation, a well as wasteincineration. Thus, a power plant can advantageously generate electricpower while, at the same time, disposing of municipal solid waste, forhighly cost-effective operation. The combustion apparatus 22 can eitherbe employed in new power plant designs, or be retrofitted to existingpower generating plants.

With reference now to FIGS. 10 and 11, a second embodiment of theinvention is in the form of a vertically-extending incinerator 350,primarily for wood and vegetation debris. The incinerator 350 of FIGS.10 and 11, like the combustion apparatus 22 of FIGS. 1-9, employs apneumatically suspended combustion zone 352 created by having streams ofcombustion air directed upwardly from a floor grate and from the sidesof a combustion chamber, and wherein relatively high combustiontemperatures are sustained by providing a high volume of excesscombustion air, the same combustion air which maintains thepneumatically suspended combustion zone 352. The incinerator 350 ofFIGS. 10-12 effects complete combustion of vegetation type debris, thusessentially eliminating "smoke".

The incinerator 350, like the combustion apparatus 22 of FIGS. 1-9,includes pressurized slotted tubes 354 defining walls 356 of acombustion chamber 358, within which is a pneumatically suspendedcombustion zone 352. A pressurized outer containment structure 360surrounds the slotted tubes 354 defining the combustion chamber 358, andair streams are forced between the slotted tubes 354 as in thecombustion apparatus 22 of FIGS. 1-9. The interiors of the hollow walltubes 352 are pressurized by a suitable ducting arrangement (not shown),and the outer containment chamber 360 is pressurized by means of ablower 362 (FIG. 11).

Above the combustion chamber 356, at the top of the incinerator 350, isan exhaust stack 364 defined by hollow, pressurized walls 366 havinghorizontal slots 368. Pressurized air supply ducts 370 and 372 supplyair to the interior of the exhaust stack 364 hollow wall 366. Below theexhaust stack 364 is a draft air intake hood 374, having openings 376through which ambient air is drawn. Combustion of any remainingparticulate matter occurs in the exhaust stack 364. High temperaturecombustion within the combustion zone 352, followed by combustion withinthe exhaust gas stack 364, results in essentially complete eliminationof smoke.

At the bottom of the combustion chamber 358 is an ash conveyor 376driven over a slotted floor grate 378 above a pressurized plenum chamber380. The conveyor 376 of the incinerator 350 is substantially identicalto the combustion chamber conveyor 70 of the embodiment of FIGS. 1-9,except that the conveyor 376 is primarily for transporting ash out ofthe combustion chamber 356, rather than assisting also in moving largeobjects through a tunnel-like combustion chamber, as in the incineratorsystem 20 of FIGS. 1-9. The floor grate plenum chamber 380 ispressurized by means of supply ducts 382 and 384, and the conveyor 376is driven by chain sprockets 386 and 388 connected by a shaft 390 anddriven by a variable speed motor 392.

The vegetation incinerator 350 of FIGS. 10 and 11 includes a conveyor394 for introducing waste material through an opening 396 and over afeedplate 398 into the combustion chamber 356. The conveyor 394 asdepicted in FIGS. 10 and 11 is a relatively simple conveyor. However, asin the embodiment of FIGS. 1-9, a more elaborate waste material conveyorsystem can be employed if desired, including preheating of wastematerial, and a tunnel-like pressurized waste material supply conveyorchamber.

Referring finally to FIG. 12, depicted is another embodiment of theinvention wherein walls 450 of a combustion chamber 452 are made of arefractory material, and include a multiplicity of openings 454 orientedgenerally towards a combustion zone, generally designated 456. Thus, thewalls 450 of the FIG. 12 embodiment are an alternative to the walls andceiling 100, 102, 104, 106 and 108 of the combustion apparatus 22 ofFIGS. 1-9 comprising slotted wall and ceiling tubes 101, 103, 105, 107and 109. In FIG. 12, a blower 458 is in gas flow communication with theopenings 454, preferably by means of a pressurized outer containmentstructure 460, comparable to the outer containment structure 34 of thecombustion apparatus 22 of FIGS. 1-9. At the bottom of the combustionchamber 452 of FIG. 13 is a conveyor and floor grate structure 462,which may be identical to the structure of FIG. 8.

During operation of the FIG. 12 embodiment, pressurized air forcedthrough the openings 454 supplies excess combustion air to thecombustion zone 456 as in the previously described embodiments, and, inaddition, keeps the heat of combustion away from the walls 450.

While specific embodiments of the invention have been illustrated anddescribed herein, it is realized that numerous modifications and changeswill occur to those skilled in the art. It is therefore to be understoodthat the appended claims are intended to cover all such modificationsand changes as fall within the true spirit and scope of the invention.

What is claimed is:
 1. Combustion apparatus comprising:walls defining acombustion chamber having a pneumatically suspended combustion zone; atleast a portion of each of said walls comprising a plurality of tubeswhich are adjacent and spaced from each other, said tubes having tubeinteriors and tube walls; said tube walls having openings orientedgenerally towards the combustion zone; at least one tube supply blowerconnected to said tubes for pressurizing said tube interiors withcombustion-supporting gas such that combustion-supporting gas streamsare directed out of said openings to at least partially define thecombustion zone and to force the heat of combustion away from saidwalls; an outer containment structure surrounding said walls; and atleast one outer containment structure supply blower connected forpressurizing said outer containment structure with combustion-supportinggas such that combustion-supporting gas streams are directed betweensaid tubes into the combustion chamber.
 2. Combustion apparatus inaccordance with claim 1, wherein said outer containment structure iszoned.
 3. Combustion apparatus in accordance with claim 2, whichcomprises a tunnel-like structure wherein solid waste material isintroduced at one end and exit ports for hot gas and ash are provided atthe other end, and wherein an outer containment structure zone isprovided at the one end to provide pressurized combustion-supporting gasat a relatively higher volume compared to other areas of the outercontainment structure in order to force gases within the combustion zonetowards the other end.
 4. Combustion apparatus in accordance with claim1, which further comprises vanes affixed to said tubes for controllingthe direction of combustion-supporting gas streams directed between saidtubes.
 5. Combustion apparatus comprising:walls defining a combustionchamber having a pneumatically suspended combustion zone; at least aportion of each of said walls comprising a plurality of adjacent tubeshaving tube interiors and tube walls; said tube walls having openingsoriented generally towards the combustion zone; at least one tube supplyblower connected to said tubes for pressurizing said tube interiors withcombustion-supporting gas such that combustion-supporting gas streamsare directed out of said openings to at least partially define thecombustion zone and to force the heat of combustion away from saidwalls; and an element for introducing material to be combusted into saidcombustion zone, and a hot combustion-supporting gas supply forpreheating the material, said element for introducing material to becombusted comprising waste material supply conveyor elements moving overa grate, and the hot combustion-supporting gas being directed upwardlythrough said grate.
 6. Combustion apparatus in accordance with claim 5,wherein said waste material supply conveyor elements are containedwithin a pressurized chamber.
 7. Combustion apparatus in accordance withclaim 6, wherein said pressurized chamber has an entry door whichreceives waste material while maintaining pressure within saidpressurized chamber.
 8. Combustion apparatus comprising:walls defining acombustion chamber having a pneumatically suspended combustion zone; atleast a portion of each of said walls comprising a plurality of adjacenttubes having tube interiors and tube walls, and said tubes comprisingsilicon carbide refractory material; said tube walls having openingsoriented generally towards the combustion zone; and at least one tubesupply blower connected to said tubes for pressurizing said tubeinteriors with combustion-supporting gas such that combustion-supportinggas streams are directed out of said openings to at least partiallydefine the combustion zone and to force the heat of combustion away fromsaid walls.